1. Field of the Invention
The present invention is in the field of digital radiography and relates to a system of supplying a processed radiographic image to a remote station such as a display station, a hard copy recorder, an archiving station etc.
2. Description of the Prior Art
In the field of digital radiography a wide variety of image acquisition techniques have been developed that render a digital representation of a radiation image.
In one of these techniques a radiation image, for example an x-ray image of an object, is stored in a screen comprising a photostimulable phosphor such as one of the phosphors described in European patent publication 503 702 published on Sep. 16, 1992.
In a read out station the stored radiation image is read by scanning the screen with stimulating radiation such as laser light of the appropriate wavelength, detecting the light emitted upon stimulation and converting the emitted light into an electric representation for example by means of an adequately adjusted photomultiplier and finally digitizing the signal.
After readout the residual image left on the photostimulable phosphor screen is erased so that the screen is again available for exposure.
The digital image signal is then processed on-line.
The image is further sent to a processing station where it can be subjected to additional processing steps.
A processing station provides a powerful tool for advanced and interactive image processing. It allows to use the capabilities of the image processing to the fullest extent. Any mistakes regarding image processing that might be introduced during identification of the cassette can be corrected and the image can be re-processed using newly set parameters.
After processing the image can be transmitted to a recorder, e.g. a laser recorder for reproduction on the film size and lay-out of the radiologist's choice and/or it can be transmitted to an archival station.
It is also common practice to display the processed image on a display station for evaluation by a radiologist.
The display station or archival station or recorder to which the processed image is supplied may be positioned in close vicinity of the read out station.
In a hospital environment however, a radiographic image of a patient that is generated in a central radiology room is often reviewed on a location remote from the radiology room.
Typically a radiographic image of a patient is needed in an intensive care unit whereas the image has been recorded in a central radiology room and the read out and processing device is installed in the vicinity of that radiology room.
Instead of printing the image and carrying the hard copy image to the intensive care unit, it is more convenient to transmit the image electronically and to display the transmitted image on a remote display station that is connected with the processing station by a network.
Alternatively the image can be transmitted electronically to a remote recorder for production of a hard copy.
Archiving may also be provided remote from the image processing unit.
The interfacing of an image processing station and a remote station of the above-named kind is generally performed by means of the following two elements: (i) a physical connection between the processing station and the remote station and (ii) a protocol implemented by both systems so as to provide control and interchange of data.
The physical connection can be realized by implementing a local area network (LAN) or a Wide area network (WAN) or by means of a serial or parallel point-to-point connection. A wide variety of suitable physical connections are available on the market: Ethernet (trademark of Xerox corporation), FDDI (Fiber distributed data interchange), RS232, SCSI, etc.
A protocol can be implemented up to different levels of the OSI seven layer model.
Suitable protocols that make data of linked systems accessible in the form of a file or as byte-streams are commercially available for numerous hardware platforms. Examples are: NFS (trademark of Sun Microsystems), TCP-IP, TLI sockets, Netware (trademark of Novell Inc.) etc.
For medical applications dedicated protocols such as ACR-NEMA, DICOM . . . or extended protocols such as SPI . . . have been developed.
But implementations of these protocols are not yet available for all platforms.
Electronic transmission between devices requires that a common protocol is used so as to enable data interchange, said protocol defining a number of commands that are identically interpreted by either of the systems.
In this particular application however, data are to be transmitted between an image processing unit and one of a great variety of remote display, archival, hard copy . . . stations available on the market. All available remote stations do not necessarily use the same protocol.
Therefore arrangements would have to be made with regard to data communication for each individual kind of remote station. This would demand for close cooperation between different parties on the level of hardware, protocols and application software.
European patent application EP 599 097 discloses an X-ray image processing apparatus that allows automatic routing of differently processed versions of an X-ray image to different, selected destinations.
This disclosure does not focus on the communication problems that might be encountered when data are to be transmitted to remote stations of different kinds and no common protocol has been agreed upon.
An additional problem relating to display stations in particular is that each of the number of display devices available on the market have their proper conversion characteristics and their proper limitations.
Hence accurate representation of grey shades may become a problem when an image is converted between an electronic device (e.g. image on disc of the processing station) and a physical medium such as a phosphor in a CRT display device.